This invention comprises an array which includes a small rigid body containing three active acoustic transducers. When employed in conjunction with existing signal detection and processing equipment, it will find the relative positions of the receiving elements. Of a large flexible acoustic array of arbitrary and changing shape. Thus a large two-or three-dimensional acoustic array may be fabricated, beamformed and processed without employing the usual large rigid structure.
Large low-frequency sonar arrays are widely used by the U.S. Navy. Beamforming and noise rejection by the array is achieved by several methods, but all methods depend on knowledge of the relative location of elements in the array.
FIG. 1 shows a 3-element line array 10. Let T.sub.d =the time required for sound to travel a distance d in the medium. If the output of element 12-3 is delayed by a time equal to 2T.sub.d and if the output of element 12-2 is delayed by a time T.sub.d, and if both are then added to the output of element 12-1, then the resulting summed signal will emphasize signals coming from a direction .+-..theta., where .theta.= arc cos d/l. It will tend to reject sound (noise) coming from other directions.
Large flexible line arrays may be towed or otherwise put in tension, and the relative location of the elements may be assumed from the tensioning devices. However, large 2-and 3-dimensional arrays are preferred over line arrays because of their improved performance and noise rejection over line arrays.
The prior art method of constructing 2-and 3-dimensional arrays was to fabricate a rigid or semi-rigid structure with a known position for each element of the array. The disadvantages of this method are the weight and cost of the rigid structure, the propagation of sound in the rigid structure which reduces the performance of the array, and the production of sound by the rigid structure (flow noise about the structure, creaking and squeaking of a portable or floating rigid structure).